I have had this ring for a number of years and found it in a jewelry box today. I can’t remember the last time I wore it or even where I got it from. I never realized that it was signed until I started looking today and I thought I saw a glimpse of some very faint letters. It took me quite a while to actually get a picture where I could see them and then even longer experimenting with photo settings to make them more easily visible. I have checked several books and online and the only FS that I am finding is Frank Smiley. The information in the reference books has been very limited. He is Navajo and I think was working in the 70s. If anyone else is familiar with him and can offer some more info, I would really appreciate knowing. Thank you all.
Nice find @Islandmomma! I like the heavy setting, and the turquoise is pretty. When I first looked at the picture of the “hallmark”, I couldn’t see anything that made sense. After you mentioned FS, I think I see what you are referring to. Somewhere back in the recesses of my brain, the name “Smiley” sounds familiar, but unfortunately I can’t recall anything helpful! I’ve also had problems with hallmarks on older, well worn pieces…it’s frustrating. Don’t give up, if the stars align, you may find out more when you least expect it
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Not sure if it’s him or not but a search turned up similar heavier FS jewelry attributed to him (or it’s the only name anyone could attach to the initials 
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Thank you and @Bmpdvm. I have checked multiple books and online and that is the only name that I have found so far with the initials FS.